As a psychedelic band led by Syd Barrett in the late 1960s, Pink Floyd had moderate mainstream success and were one of the most popular bands in the London underground music scene;[5] however, Barrett's erratic behaviour eventually forced his colleagues to replace him with guitarist and singer David Gilmour.[1] After Barrett's departure, the band released Ummagumma. The album was released as a double disc, the first disc containing songs performed live, the second containing new studio-recorded songs. Singer and bass player Roger Waters gradually became the dominant and driving force in the mid-1970s, until his departure from the group in 1985.[1] The band recorded several albums, achieving worldwide success with The Dark Side of the Moon (1973), Wish You Were Here (1975), Animals (1977), and The Wall (1979); all except Animals reached number one in the US. The Dark Side of the Moon is one of the best-selling albums in the world[6] and The Wall is the highest-certified multiple-disc album by the Recording Industry Association of America.[7] In 1986, Waters declared Pink Floyd "a spent force" and sued to dissolve their partnership and retire the name Pink Floyd, but the remaining members, led by Gilmour, continued recording and touring under the name Pink Floyd.[1] Following an out-of-court settlement, the band enjoyed worldwide success with A Momentary Lapse of Reason (1987), The Division Bell (1994) and The Endless River (2014).[8]